Vacuum insulating glass (VIG) units typically include at least two spaced apart glass substrates that enclose an evacuated or low-pressure space/cavity therebetween. The substrates are interconnected by a peripheral edge seal and typically include spacers between the glass substrates to maintain spacing between the glass substrates and to avoid collapse of the glass substrates that may be caused due to the low pressure environment that exists between the substrates. Some example VIG configurations are disclosed, for example, in U.S. Pat. Nos. 5,657,607, 5,664,395, 5,657,607, 5,902,652, 6,506,472 and 6,383,580, the disclosures of which are all hereby incorporated by reference herein in their entireties.
FIGS. 1 and 2 illustrate a typical VIG window unit 1 and elements that form the VIG window unit 1. For example, VIG unit 1 may include two spaced apart substantially parallel glass substrates 2, 3, which enclose an evacuated low-pressure space/cavity 6 therebetween. Glass sheets or substrates 2,3 are interconnected by a peripheral edge seal 4 which may be made of fused solder glass, for example. An array of support pillars/spacers 5 may be included between the glass substrates 2, 3 to maintain the spacing of substrates 2, 3 of the VIG unit 1 in view of the low-pressure space/gap 6 present between the substrates 2, 3.
A pump-out tube 8 may be hermetically sealed by, for example, solder glass 9 to an aperture/hole 10 that passes from an interior surface of one of the glass substrates 2 to the bottom of an optional recess 11 in the exterior surface of the glass substrate 2, or optionally to the exterior surface of the glass substrate 2. A vacuum is attached to pump-out tube 8 to evacuate the interior cavity 6 to a low pressure, for example, using a sequential pump down operation. After evacuation of the cavity 6, a portion (e.g., the tip) of the tube 8 is melted to seal the vacuum in low pressure cavity/space 6. The optional recess 11 may retain the sealed pump-out tube 8. Optionally, a chemical getter 12 may be included within a recess 13 that is disposed in an interior face of one of the glass substrates, e.g., glass substrate 2. The chemical getter 12 may be used to absorb or bind with certain residual impurities that may remain after the cavity 6 is evacuated and sealed.
VIG units with fused solder glass peripheral edge seals 4 are typically manufactured by depositing glass frit, in a solution (e.g., frit paste), around the periphery of substrate 2 (or on substrate 3). This glass frit paste ultimately forms the glass solder edge seal 4. The other substrate (e.g., 3) is brought down on substrate 2 so as to sandwich spacers/pillars 5 and the glass frit solution between the two substrates 2, 3. The entire assembly including the glass substrates 2, 3, the spacers/pillars 5 and the seal material (e.g., glass frit in solution or paste), is then heated to a temperature of at least about 500° C., at which point the glass frit melts, wets the surfaces of the glass substrates 2, 3, and ultimately forms a hermetic peripheral/edge seal 4.
After formation of the edge seal 4 between the substrates, a vacuum is drawn via the pump-out tube 8 to form low pressure space/cavity 6 between the substrates 2, 3. The pressure in space 6 may be produced by way of an evacuation process to a level below atmospheric pressure, e.g., below about 10−2 Torr. To maintain the low pressure in the space/cavity 6, substrates 2, 3 are hermetically sealed. Small high strength spacers/pillars 5 are provided between the substrates to maintain separation of the approximately parallel substrates against atmospheric pressure. As noted above, once the space 6 between substrates 2, 3 is evacuated, the pump-out tube 8 may be sealed, for example, by melting its tip using a laser or the like.
After evacuation of the cavity to a pressure less than atmospheric, sealing of the pump-out tube may be accomplished by heating an end of the pump-out tube that is used to evacuate or purge the cavity to melt the opening and thus seal the cavity of the VIG window unit. For example and without limitation, this heating and melting may be accomplished by laser irradiation of the tip of the pump-out tube.
In some instances breakage of the VIG unit glass in the vicinity of the edge seal during the cavity evacuation process was observed. Significant time and resources were expended in an effort to determine the cause of such breakage during cavity evacuation. It was ultimately recognized that seal height variations may be related to the breakage problems. For example, it may sometimes be the case that the material used to form the edge seal, such as, for example, an adhesive containing frit material, or the like, may include too large of variations in height about the perimeter of the seal that defines the cavity. After conducting numerous experiments, it was surprisingly found that a correlation existed between the seal thickness variation tolerance and instances of breakage during the cavity evacuation (or pump-down) process. It was also surprisingly found that these variations in seal height influence the amount of stress on the VIG units in the vicinity of the seal during the process of evacuating the cavity formed between the glass substrates of the VIG unit. This evacuation process may sometimes be referred to as a pull-down or pump-down procedure. It was also surprisingly found that too large of variations in the seal height sometimes results in sufficient stress during pump-down that the glass of the VIG unit inside the perimeter of and generally in the vicinity of the seal would break. For example, and without limitation, too much variation of the seal height resulted in a gap between the pillars or spacers and at least one of the glass substrates, which allowed the glass substrate to bend or flex during pump-down. The glass was found to break if the variation in seal height about the perimeter of the seal was too great.
It was also found that there may be several causes for resulting large seal height variations. These may include, for example, and without limitation, the degree of uniformity of the initial application of green (e.g., unfired) seal material (e.g., frit), and warping or bending of the glass substrates during the firing process. Both of these conditions were found to contribute to a large degree of variation (e.g., non-uniformity) of final seal height.
To overcome drawbacks associated with glass breakage due to glass bending or flexing during pump-down, it was further determined that reducing variations in seal height about the perimeter of the edge seal resulted in mitigating the stress (e.g., reducing an amount of bend or flex in the glass substrate) on the VIG unit during pump down and reduced the instances of breakage of the VIG unit glass during pump-down. As a result of experimentation, seal height variation or tolerance was able to be reduced to small levels by, for example, and without limitation, controlling the initial dispensed height of the seal material (e.g., frit material), controlling the flow of the seal material during firing and controlling temperature uniformity during the sealing process. For example, and without limitation, it was found that controlling final edge seal height variations to preferably be less than about 0.20 mm, more preferably less than about 0.15 mm and even more preferably less than about 0.10 mm, resulted in significantly reduced glass breakage during pump-down. It may also be advantageous to provide a firing process that reduced warping of the glass substrates during firing and controlled and also controlled flow of the seal material, which may also contribute to reducing edge seal height variation.
In order to achieve lower final edge seal height variations, the inventors found, for example, and without limitation, that controlling the initial dispensed height of the unfired seal material using a machine application process provided significantly improved final seal height uniformity such that the final seal height variations are in acceptable ranges as noted above. In addition, for example, controlling temperature uniformity during firing reduced the amount of warping or bending of the glass substrates, further reducing variations in final seal height. Moreover, controlling the flow of the seal material during firing, for example, also improved the final seal height variations, such as, for example, by performing a longer firing process that allows the seal material to flow to match the height of the pillars/spacers during firing.
These and other advantages are provided by a vacuum insulated glass window unit comprising: a first substrate and a second substrate; a seal material sandwiched between the first and second substrates and defining a periphery of a cavity formed between the first and second substrates, and forming a hermetic seal between the first and second substrates, wherein a variation in a height of the seal material around the low pressure cavity is preferably less than about 0.20 mm, more preferably less than or equal to about 0.15 mm, and even more preferably less than or equal to about 0.10 mm.
Further advantages are provided by a method of making a vacuum insulated glass window unit comprising: depositing a seal material on a first substrate, said seal material having a perimeter, the seal material being deposited by a machine and having an unfired height in a range of about 0.6 mm to 0.9 mm; and firing a subassembly comprising said first substrate, a second substrate and the seal material sandwiched between the first and second substrates to provide a vacuum insulated glass window unit subassembly having a fired seal material height variation of preferably less than about 0.20 mm, more preferably less than or equal to about 0.15 mm, and even more preferably less than or equal to about 0.10 mm.
These and other embodiments and advantages are described herein with respect to certain example embodiments and with reference to the following drawings in which like reference numerals refer to like elements, and wherein: